CONTROL OF NATURE

Hauraki Plains Gazette, Volume 48, Issue 2817, 3 October 1938, Page 8

CONTROL OF NATURE

COUNTERS FOR DISEASE The recently revealed use of swans by a Manchester textile factory to consume spawn which came during the drought in emergency supplies of water and stained textiles was a homely example of biological control, says the Manchester Guardian. Ordinarily, of course, this branch of science belongs to entomologists, because only insects are —as a geneial rule —sufficiently selective in their feeding habits to be safely and effectively used as controlling agents. However, reference was made a few months ago to the employment of toads to control a sugar-cane pestin Hawaii, Queensland, Mauritius, and elsewhere —and two other exceptions to the rough rule may now be mentioned. A little while back the Government of Madagascar sent a present of a fresh-water crayfish by air to the Government of Nyasaland. It had been found that dysentery and bilharzia, though rife in East Africa, were happily absent from Madagascar, and the island’s immunity was traced to its crayfish, which by eating certain snails, interrupted the life cycles of the dysentery amoeba and the bilharzia fluke-worm. So now the , Madagascan crayfish are creeping about the beds of Nyasaland’s rivers in search of snails. The othei’ enterprise of this kind has been conducted with a kind of small fish, of the genus Gambusia, from North America. These fish have been exported to and settled in Spain, Italy, Russia and India, in an attempt to control the mosquitoes which spread malaria. The fish are said to have proved useful in small collections of water, but where there are large expanses they are much less effective.

That human diseases —instead of plant or visible insect pests—should be the object of biological control campaigns is itself an interesting development, for “b.c.” is a modern branch of science, scarcely fifty years old. It may be pointed out that Kirby and Spence recognised, so long ago as 1816, that the aphids attacking hops and other plants could be controlled if only ladybirds could be increased at will. And certain ladybirds are now bred in large numbers for use in various countries. Yet

gardeners have still to find an economic way of breeding the English ladybirds, which do such yood work against greenfly.